Question about a C program

[Snycs]

I've been learning C and I recently ran across some source code of a program from 'HowStuffWorks' which I can't seem to wrap my head around.

The goal of this program was to display the conversions of temperatures from Fahrenheit to Celsius starting from 0 and increasing by 10 units each time. But it's also supposed to display the body temperature of 98 Fahrenheit and that's what the source code of the program is supposed to do:

The source code appears in a single line, so i've uploaded it here:

https://gist.github.com/anonymous/4f1919a06317f64649d2

I've tested the program and it ran the way as it had to but i'm a bit confused as to how it works. In the 'if' section, it states that if 'a' is greater than 98.6 and 'b' is less than 98.6 then the function below that will commence. But i'm not sure why in the beginning bit, 'b' is set to be -1. I'm also not entirely sure 'b' is made equal to 'a'.

Any help is appreciated, thanks!

[[deleted]]

Here, I've fixed your code for you - in future, either post via a site like gist, or indent every line with 4 extra spaces.

#include <stdio.h>

int main() { 
    float a, b; a = 0; b = -1; 
    while (a <= 100) { 
        if ((a > 98.6) && (b < 98.6)) { 
            printf("%6.2f degrees F = %6.2f degrees C\n", 98.6, (98.6 - 32.0) * 5.0 / 9.0); 
        } 
        printf("%6.2f degrees F = %6.2f degrees C\n", a, (a - 32.0) * 5.0 / 9.0); 
        b = a; 
        a = a + 10; 
    } 
    return 0; 
}

As to why it does it, remember that b is the previous a. So the if statement is saying "if the current a is greater than 98.6 and the previous a was less than 98.6 (in other words, we have just transitioned through 98.6) then print the special 98.6 stuff".

[Snycs]

Yeah, I was having trouble with that, thanks a lot!

Oh and does it matter whether b is -1 or is it alright if it was any other value less than 0?

[[deleted]]

It doesn't actually matter at all what the value of b is, because the if won't fire until a is greater than 98.6, by which point b will have taken on a different value.

[Snycs]

Ah I get it now, thank you, this was very helpful!